Green curable ink

ABSTRACT

A lightfast green radiation curable ink including at least one curable monomer, at least one organic gellant, at least one photoinitiator and at least one colorant, where the colorant exhibits a reflectance on a substrate at a loading of from about 2 mg/inch 2  to about 7 mg/inch 2  that ranges from 50% to about 60% at a wavelength of 500 nm and that ranges from 0% to about 10% at a wavelength of about 600 nm which substantially matches Pantone green.

TECHNICAL FIELD

The disclosure is directed to curable inks, such as, radiation-curableinks, and use thereof in forming images, such as through inkjetprinting. More specifically, the disclosure is directed to greenradiation-curable gel inks, where such inks match the color propertiesof the Pantone primary Pantone Green, methods of making such inks, andmethods of forming images with such inks

BACKGROUND INFORMATION

Inkjet printing systems and radiation-curable gel inks are known in theart. However, a need remains for improved gel ink compositions fordeveloping higher quality images with greater color range.

Gel ink colors typically include, for example, cyan, magenta, yellow andblack. Gel ink compositions covering more of the green region of thecolor spectrum are desirable.

SUMMARY OF THE INVENTION

The present disclosure, in embodiments, addresses those various needsand problems by providing green color radiation curable inks.

In embodiments, a green radiation-curable gel ink is disclosedincluding: at least one curable monomer, at least one organic gellant,at least one photoinitiator and at least one colorant, wherein the inkexhibits a reflectance on a substrate at a loading of from about 2mg/inch² to about 7 mg/inch² that ranges from 50% to about 60% at awavelength of 500 nm and that ranges from 0% to about 10% at awavelength of about 600 nm.

In embodiments, a method of making a green radiation-curable ink isdisclosed including: mixing at least one curable monomer, at least oneorganic gellant, at least one photoinitiator and at least one colorant,wherein the ink exhibits a reflectance on a substrate at a loading offrom about 2 mg/inch² to about 7 mg/inch² that ranges from 50% to about60% at a wavelength of 500 nm and that ranges from 0% to about 10% at awavelength of about 600 nm; heating the mixture; and cooling the heatedmixture to form a gel ink, where the resulting ink matches PANTONE®Green in colour within a ΔE2000 of about 3 or less.

Those and other improvements are accomplished by the compositions andmethods described in embodiments herein.

DETAILED DESCRIPTION OF THE INVENTION

This disclosure is not limited to particular embodiments describedherein, and some components and processes may be varied by one ofordinary skill, based on the disclosure.

In digital imaging, colored inks generally are used by printing halftonedots in varying concentrations and combinations to form the desiredimage. While the halftone dots typically small enough so as not to bevisible, the texture produced by the dots can be visible and may beunacceptable for certain high quality applications, such as, printinghigh quality photographs. In addition to objectionable halftone texture,even small levels of nonuniformity can lead to objectionable visiblenoise, such as graininess, mottle, etc. The objectionable visibletexture and noise may be reduced by using of colored inks that accesscolors in the green region.

Image quality may be improved by adding one, two or more additional inksto form a system with five, six or more print heads. One color of ink ofvalue and which will increase image quality is a PANTONE® printingprimary, including, for example, PANTONE® Green.

The PANTONE® Matching System of 14 color primaries may be viewed interms of ΔE, a single number that represents the ‘distance’ between twocolors. A ΔE₂₀₀₀ of 2 to 3 generally is considered to be at the limit ofvisual perception.

An advantage of radiation-curable inks is the reduced jetting andgelling temperatures as compared to previous, standard hot melt inkjetinks Standard hot melt inkjet inks must be jetted at high temperatures,whereas the presently disclosed inkjet ink compositions may exhibit geland lower jetting temperatures. Lower gel temperatures can furtherfacilitate smoothing or leveling of the jetted ink by the application ofheat.

In this specification and the claims that follow, singular forms such as“a,” “an,” and “the” include plural forms unless the content clearlydictates otherwise.

All ranges disclosed herein include, unless specifically indicated, allendpoints and intermediate values. Unless otherwise indicated, allnumbers expressing quantities, conditions and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term, “about.” “About,” is meant to indicate avariation of no more than 20% from the stated value. Also used herein isthe term, “equivalent,” “similar,” “essentially,” “substantially,”“approximating” and “matching,” or grammatic variations thereof, havegenerally acceptable definitions or at the least, are understood to havethe same meaning as, “about.”

As used herein, “lightfastness” refers to the degree to which a dyeresists fading due to light exposure. The Blue Wool Scale measures andcalibrates the permanence of coloring dyes. Traditionally this test wasdeveloped for the textile industry but now has been adopted by theprinting industry as measure of lightfastness of ink colorants.

Normally two identical dye samples are created. One is placed in thedark as the control and the other is placed in the equivalent ofsunlight for a 3 month period. A standard bluewool textile fading testcard is also placed under the same light conditions as the sample undertest. The amount of fading of the sample then is assessed by comparisonto the original color.

A rating between 0 and 8 is awarded by identifying which one of theeight strips on the bluewool standard card has faded to the same extentas the sample under test. Zero denotes extremely poor color fastnesswhilst a rating of eight is deemed not to have altered from the originaland thus credited as being lightfast and permanent. For an ink ofinterest, a lightfastness of about 6 or greater, about 7 or greater,about 8 or greater is desirable. In embodiments, lightfastness can bedetermined using devices available, for example, from Microscal Co.,London, UK or Q-Lab Corp, Cleveland, Ohio.

The term, “functional group,” refers, for example, to a group of atomsarranged in a way that determines the chemical properties of the groupand the molecule thereto. Examples of functional groups include halogenatoms, hydroxyl groups, carboxylic acid groups and the like.

The term, “short-chain,” refers, for example, to hydrocarbon chains of asize, “n,” in which n represents the number of carbon atoms in the chainand wherein n is a number of from about 1 to about 7, from about 2 toabout 6, from about 3 to about 5.

The term, “curable,” describes, for example, a material that may becured via polymerization, including, for example, free radical routes,and/or in which polymerization is photoinitiated though use of aradiation-sensitive photoinitiator. The term, “radiation-curable,”refers, for example, to all forms of curing on exposure to a radiationsource, including light and heat sources and including in the presenceor absence of initiators. Exemplary radiation-curing techniques include,but are not limited to, curing using ultraviolet (UV) light, for examplehaving a wavelength of 200-400 nm or more rarely visible light,optionally, in the presence of photoinitiators and/or sensitizers,curing using electron-beam radiation, optionally, in the absence ofphotoinitiators, curing using thermal curing, in the presence or absenceof high-temperature thermal initiators (and which may be largelyinactive at the jetting temperature) and appropriate combinationsthereof.

As used herein, the term, “viscosity,” refers to a complex viscosity,which is the measurement that can be provided by a mechanical rheometerthat subjects a sample to a steady shear strain or a small amplitudesinusoidal deformation. The shear strain is applied by the operator tothe motor and the sample deformation (torque) is measured by thetransducer. Alternatively, a controlled-stress instrument, where theshear stress is applied and the resultant strain is measured, may beused. Such a rheometer provides a periodic measurement of viscosity atvarious plate rotation frequencies, ω, rather than the transientmeasurement of, for instance, a capillary viscometer. The reciprocatingplate rheometer measures both the in phase and out of phase fluidresponse to stress or displacement. The complex viscosity, η*, isdefined as η*−η′−iη″; where η′=G″/ω, η″=G′/ω and i is −1. Alternativelya viscometer that can measure only the transient measurement of, forinstance, a capillary or shear viscosity can also be used.

“Optional,” or, “optionally,” refers, for example, to instances in whichsubsequently described circumstance may or may not occur, and includeinstances in which the circumstance occurs and instances in which thecircumstance does not occur.

The terms, “one or more,” and, “at least one,” refer, for example, toinstances in which one of the subsequently described circumstancesoccurs, and to instances in which more than one of the subsequentlydescribed circumstances occur.

“Substrate,” refers to a material onto which an ink is applied. Forexample, paper, metal, plastic, a membrane or combination thereof, wouldbe considered substrates.

“Double MEK Rub,” refers to an Evaluation for Solvent Resistance bySolvent Rub Test—ASTM D4752 and NCCA 11-18. The test method is used todetermine the degree of cure of an ink by the ink resistance to aspecified solvent. The solvent rub test usually is performed usingmethyl ethyl ketone (MEK) as the solvent. ASTM D4752 involves rubbingthe surface of a surface containing the ink with cheesecloth soaked withMEK until failure or breakthrough of the ink occurs. The type ofcheesecloth, the stroke distance, the stroke rate and approximateapplied pressure of the rub are specified. The rubs are counted as adouble rub (one rub forward and one rub backward constitutes a doublerub).

Monomers

In embodiments, the ink composition may include one or more monomers orcomonomers. The combination of the monomers or comonomers may aid insolubilizing the gellant material. The monomers or comonomers may bechosen from any suitable radiation-curable monomers.

In embodiments, ink compositions may comprise a first monomer, due tothe solubility and gelling properties of gellant materials, such as,epoxy-polyamide composite gellants, which are useful for producing inkcompositions including an ink vehicle having a thermally-driven andreversible gel phase, where the ink vehicle is comprised of curableliquid monomers, such as UV-curable liquid monomers. The gel phase ofsuch ink compositions allows an ink droplet to be pinned to a receivingsubstrate.

Examples of the curable monomer of the composition of interest includepropoxylated neopentyl glycol diacrylate (such as SR-9003 fromSartomer), diethylene glycol diacrylate, triethylene glycol diacrylate,hexanediol diacrylate, dipropyleneglycol diacrylate, tripropylene glycoldiacrylate, epoxylated neopentyl glycol diacrylate, isodecyl acrylate,tridecyl acrylate, isobornyl acrylate, isobornyl(meth)acrylate,propoxylated trimethylolpropane triacrylate, ethoxylatedtrimethylolpropane triacrylate, di-trimethylolpropane tetraacrylate,dipentaerythritol pentaacrylate, ethoxylated pentaerythritoltetraacrylate, propoxylated glycerol triacrylate, isobornylmethacrylate, lauryl acrylate, lauryl methacrylate, neopentyl glycolpropoxylate methylether monoacrylate, isodecylmethacrylate, caprolactoneacrylate, 2-phenoxyethyl acrylate, isooctylacrylate,isooctylmethacrylate, mixtures thereof and the like. As relativelynon-polar monomers, mention may be made of isodecyl(meth)acrylate,caprolactone acrylate, 2-phenoxyethyl acrylate, iso octyl(meth)acrylateand butyl acrylate. In addition, multifunctional acrylatemonomers/oligomers may be used not only as reactive diluents but also asmaterials that can increase the cross-link density of the cured image,thereby enhancing the toughness of the cured images.

The term, “curable monomer,” is also intended to encompass curableoligomers, which may also be used in the composition. Examples ofsuitable radiation-curable oligomers that may be used in thecompositions have a low viscosity, for example, from about 50 cPs toabout 10,000 cPs, from about 75 cPs to about 7,500 cPs, from about 100cPs to about 5,000 cPs. Examples of such oligomers may include CN549,CN131, CN131B, CN2285, CN 3100, CN3105, CN132, CN133, CN132, availablefrom Sartomer Company, Inc., Exeter, Pa., EBECRYL 140, EBECRYL 1140,EBECRYL 40, EBECRYL 3200, EBECRYL 3201, EBECRYL 3212, available fromCytec Industries Inc, Smyrna Ga., PHOTOMER 3660, PHOTOMER 5006F,PHOTOMER 5429, PHOTOMER 5429F, available from Cognis Corporation,Cincinnati, Ohio, LAROMER PO 33F, LAROMER PO 43F, LAROMER PO 94F,LAROMER UO 35D, LAROMER PA 9039V, LAROMER PO 9026V, LAROMER 8996,LAROMER 8765, LAROMER 8986, available from BASF Corporation, FlorhamPark, N.J., and the like. As multifunctional acrylates andmethacrylates, mention may also be made of pentaerythritoltetra(meth)acrylate, 1,2 ethylene glycol di(meth)acrylate, 1,6hexanediol di(meth)acrylate, 1,12-dodecanol di(meth)acrylate,tris(2-hydroxy ethyl)isocyanurate triacrylate, propoxylated neopentylglycol diacrylate, hexanediol diacrylate, tripropylene glycoldiacrylate, dipropylene glycol diacrylate, amine-modified polyetheracrylates (available as PO 83 F, LR 8869, and/or LR 8889 (all availablefrom BASF Corporation)), trimethylolpropane triacrylate, glycerolpropoxylate triacrylate, dipentaerythritol penta-/hexa-acrylate,ethoxylated pentaerythritol tetraacrylate (available from Sartomer Co.Inc. as SR 494) and the like.

In embodiments, the monomers may be chosen from short-chain alkyl glycoldiacrylates or ether diacrylates, such as, propoxylated neopentyl glycoldiacrylate, or from acrylates having short-chain alkyl estersubstituents, such as, caprolactone acrylate, and the commerciallyavailable products CD536, CD 2777, CD585 and CD586 (available fromSartomer Co. Inc.).

In embodiments, the radiation-curable gel ink compositions may includeone or more monomers in an amount ranging from about 10% to about 80% byweight of the ink, from about 20% to about 70%, from about 30% to about60%.

In embodiments, to enable curing of unsaturated polymers, the inks ofthe present disclosure may also contain a photoinitiator that can be,for example, a polymeric or oligomeric hydroxy ketone. It has been foundthat such photoinitiators provide surprising results of not altering thecoloristic properties of the inks and not depressing the glasstransition temperature of the resin that may lead to blocking orcohesion problems, contrary to results that are provided by otherphotoinitiators. Furthermore, some or all of the polymeric or oligomerichydroxy ketone photoinitiators are safe for such applications as foodpackaging and the like, being FDA approved. Examples of suitablepolymeric or oligomeric hydroxy ketone photoinitiators includeoligo[2-hydroxy-2-methyl-1-[4-1 methylvinyl)phenyl]propanone] compoundsof the formula:

where R is H, CH₃ or an alkyl radical represented by C_(n)H_(2n+1) inwhich n is a positive integer from 2 to about 1000. Commercial examplesof such polymeric or oligomeric hydroxy ketone photoinitiators includethe ESACURE® photoinitiators available from Lamberti (Sartomer) Company,Inc., such as, ESACURE® One series (ESACURE® One 75, ESACURE® One 65)and the ESACURE® KIP series (KIP 150, KIP 75LT, KIP IT, KIP 100 F).Mixtures of two or more such polymeric or oligomeric hydroxy ketonephotoinitiators, or one or more polymeric or oligomeric hydroxy ketonephotoinitiator and one or more conventional photoinitiator, can also beused.

Gellant

An ink of interest can comprise at least one gellant, or gelling agent,which functions at least to increase the viscosity of the inkcomposition within a desired temperature range. For example, the gellantcan form a solid-like gel in the ink composition at temperatures belowthe gel point of the gellant, for example below the temperature at whichthe ink composition is applied.

The gel phase typically comprises a solid-like phase and a liquid phasein coexistence, wherein the solid-like phase forms a three-dimensionalnetwork structure throughout the liquid phase and prevents the liquidphase from flowing at a macroscopic level. Hence, viscosity of an inkcomposition in the solid-like phase can range from about 10⁴ to about10⁸ cPs, from about 10³ to about 10⁷ cPs, from about 10^(3.5) to about10^(6.5) cPs. The ink composition exhibits a thermally reversibletransition between the gel state and the liquid state when thetemperature is varied above or below the gel point of the inkcomposition. This temperature is generally referred to as a sol-geltemperature. The cycle of gel reformation can be repeated a number oftimes since the gel is formed by physical, non-covalent interactionsbetween the gelling agent molecules, such as, hydrogen bonding, aromaticinteractions, ionic bonding, coordination bonding, London dispersioninteractions and the like. Stimulation by physical forces, such as,temperature or mechanical agitation or chemical forces such as pH orionic strength, can cause reversible transition from liquid tosemi-solid state at the macroscopic level.

The temperature at which the ink composition is in gel state is, forexample, approximately from about 15° C. to about 55° C., from about 15°C. to about 50° C. The gel ink composition may liquefy at temperaturesof from about 60° C. to about 90° C., from about 70° C. to about 85° C.In cooling from the application temperature liquid state to the gelstate, the ink composition undergoes a significant viscosity increase.The viscosity increase can be at least three orders of magnitude, atleast a four order of magnitude increase in viscosity.

The phase change nature of the gellant can thus be used to cause a rapidviscosity increase in the jetted ink composition on the substratefollowing jetting of the ink to the substrate. In particular, jetted inkdroplets would be pinned into position on a receiving substrate, such asan image-receiving medium (for instance, paper), that is at atemperature cooler than the ink-jetting temperature of the inkcomposition through the action of a phase change transition in which theink composition undergoes a significant viscosity change from a liquidstate to a gel state (or semi-solid state).

In embodiments, the temperature at which the ink composition forms thegel state is any temperature below the jetting temperature of the inkcomposition, for example any temperature that is about 15° C. or morebelow, about 10° C. or more below, about 5° C. or more below the jettingtemperature of the ink composition. There is a rapid and large increasein ink viscosity on cooling from the jetting temperature at which theink composition is in a liquid state to the gel transition temperaturewhen the ink composition converts to the gel state.

A suitable gellant for the ink composition would gel themonomers/oligomers in the ink vehicle quickly and reversibly, anddemonstrate a narrow phase change transition, for example, within atemperature range of about 10° C. to about 85° C. The gel state ofexemplary ink compositions can exhibit a minimum of about 10² mPa·s,about 10²⁵ mPa·s, about 10³ mPa·s increase in viscosity at substratetemperatures, for instance, from about 30° C. to about 60° C., ascompared to the viscosity at the jetting temperature. Thegellant-containing ink compositions increase in viscosity within about5° C. to about 10° C. below the jetting temperature and ultimately reacha viscosity above about 10⁴ times the jetting viscosity, above about10⁴, above about 10⁶ times the jetting viscosity.

Gellants include a curable gellant comprised of a curable amide, acurable polyamide-epoxy acrylate component and a polyamide component; acurable composite gellant comprised of a curable epoxy resin and apolyamide resin, mixtures thereof and the like, as disclosed in U.S.Publ. No. 20100304040, which hereby is incorporated herein by referencein entirety. Inclusion of the gellant in the composition permits thecomposition to be applied over or on a substrate, such as, on one ormore portions of a substrate and/or on one or more portions of an imagepreviously formed on a substrate, without excessive penetration into thesubstrate because the viscosity of the composition increases as thecomposition cools following application. Excessive penetration of aliquid into a porous substrate, such as paper, can lead to anundesirable decrease in substrate opacity. The curable gellant may alsoparticipate in the curing of monomer(s) of the composition.

The gellants suitable for use in the composition may be amphiphilic innature to improve wetting, for example, when the composition is utilizedover a substrate having silicone or other oil thereon. For example, thegellants may have long, non-polar hydrocarbon chains and polar amidelinkages.

Amide gellants suitable for use include those described in U.S. Pat.Nos. 7,531,582, 7,276,614 and 7,279,587, the entire disclosure of eachof which is incorporated herein by reference.

As described in U.S. Pat. No. 7,279,587, the amide gellant may be acompound of the formula:

wherein: R₁ is:

(i) an alkylene group (wherein an alkylene group is a divalent aliphaticgroup or alkyl group, including linear and branched, saturated andunsaturated, cyclic and acyclic, and substituted and unsubstitutedalkylene groups, and wherein heteroatoms, such as, oxygen, nitrogen,sulfur, silicon, phosphorus, boron and the like either may or may not bepresent in the alkylene group) having from 1 carbon atom to about 12carbon atoms, from 1 carbon atom to about 8 carbon atoms, from 1 carbonatom to about 5 carbon atoms;

(ii) an arylene group (wherein an arylene group is a divalent aromaticgroup or aryl group, including substituted and unsubstituted arylenegroups, and wherein heteroatoms, such as, oxygen, nitrogen, sulfur,silicon, phosphorus, boron and the like either may or may not be presentin the arylene group) having from 1 carbon atom to about 15 carbonatoms, from about 3 carbon atoms to about 10 carbon atoms, from about 5carbon atoms to about 8 carbon atoms;

(iii) an arylalkylene group (wherein an arylalkylene group is a divalentarylalkyl group, including substituted and unsubstituted arylalkylenegroups, wherein the alkyl portion of the arylalkylene group can belinear or branched, saturated or unsaturated, and cyclic or acyclic, andwherein heteroatoms, such as, oxygen, nitrogen, sulfur, silicon,phosphorus, boron and the like either may or may not be present ineither the aryl or the alkyl portion of the arylalkylene group) havingfrom about 6 carbon atoms to about 32 carbon atoms, from about 6 carbonatoms to about 22 carbon atoms, from about 6 carbon atoms to about 12carbon atoms; or

(iv) an alkylarylene group (wherein an alkylarylene group is a divalentalkylaryl group, including substituted and unsubstituted alkylarylenegroups, wherein the alkyl portion of the alkylarylene group can belinear or branched, saturated or unsaturated, and cyclic or acyclic, andwherein heteroatoms, such as, oxygen, nitrogen, sulfur, silicon,phosphorus, boron and the like either may or may not be present ineither the aryl or the alkyl portion of the alkylarylene group) havingfrom about 5 carbon atoms to about 32 carbon atoms, from about 6 carbonatoms to about 22 carbon atoms, from about 7 carbon atoms to about 15carbon atoms,

wherein the substituents on the substituted alkylene, arylene,arylalkylene and alkylarylene groups can be halogen atoms, cyano groups,pyridine groups, pyridinium groups, ether groups, aldehyde groups,ketone groups, ester groups, amide groups, carbonyl groups, thiocarbonylgroups, sulfide groups, nitro groups, nitroso groups, acyl groups, azogroups, urethane groups, urea groups, mixtures thereof and the like,wherein two or more substituents can be joined together to form a ring;

R₂ and R₂′ each, independently of the other, is:

(i) alkylene groups having from 1 carbon atom to about 54 carbon atoms,from 1 carbon atom to about 48 carbon atoms, from 1 carbon atom to about36 carbon atoms;

(ii) arylene groups having from about 5 carbon atoms to about 15 carbonatoms, from about 5 carbon atoms to about 13 carbon atoms, from about 5carbon atoms to about 10 carbon atoms;

(iii) arylalkylene groups having from about 6 carbon atoms to about 32carbon atoms, from about 7 carbon atoms to about 33 carbon atoms, fromabout 8 carbon atoms to about 15 carbon atom; or

(iv) alkylarylene groups having from about 6 carbon atoms to about 32carbon atoms, from about 6 carbon atoms to about 22 carbon atoms, fromabout 7 carbon atoms to about 15 carbon atoms;

wherein the substituents on the substituted alkylene, arylene,arylalkylene and alkylarylene groups may be halogen atoms, cyano groups,ether groups, aldehyde groups, ketone groups, ester groups, amidegroups, carbonyl groups, thiocarbonyl groups, phosphine groups,phosphonium groups, phosphate groups, nitrile groups, mercapto groups,nitro groups, nitroso groups, acyl groups, acid anhydride groups, azidegroups, azo groups, cyanato groups, urethane groups, urea groups,mixtures thereof, and the like, and wherein two or more substituents maybe joined together to form a ring;

R₃ and R₃′ each, independently of the other, is either:

(a) a photoinitiating group, such as, a group derived from1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methylpropan-1-one, of theformula

groups derived from 1-hydroxycyclohexylphenylketone, of the formula

groups derived from 2-hydroxy-2-methyl-1-phenylpropan-1-one, of theformula

groups derived from N,N-dimethylethanolamine orN,N-dimethylethylenediamine, of the formula

or the like, or:

(b) a group which is:

(i) an alkyl group (including linear and branched, saturated andunsaturated, cyclic and acyclic, and substituted and unsubstituted alkylgroups, and wherein heteroatoms, such as, oxygen, nitrogen, sulfur,silicon, phosphorus, boron and the like either may or may not be presentin the alkyl group) having from about 2 carbon atoms to about 100 carbonatoms, from about 3 carbon atoms to about 60 carbon atoms, from about 4carbon atoms to about 30 carbon atoms;

(ii) an aryl group (including substituted and unsubstituted aryl groups,and wherein heteroatoms, such as, oxygen, nitrogen, sulfur, silicon,phosphorus, boron and the like either may or may not be present in thearyl group) having from about 5 carbon atoms to about 100 carbon atoms,from about 5 carbon atoms to about 60 carbon atoms, from about 6 carbonatoms to about 30 carbon atoms, such as phenyl or the like;

(iii) an arylalkyl group (including substituted and unsubstitutedarylalkyl groups, wherein the alkyl portion of the arylalkyl group canbe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms, such as, oxygen, nitrogen, sulfur, silicon,phosphorus, boron and the like either may or may not be present ineither the aryl or the alkyl portion of the arylalkyl group) having fromabout 5 carbon atoms to about 100 carbon atoms, from about 5 carbonatoms to about 60 carbon atoms, from about 6 carbon atoms to about 30carbon atoms, such as benzyl or the like; or

(iv) an alkylaryl group (including substituted and unsubstitutedalkylaryl groups, wherein the alkyl portion of the alkylaryl group canbe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms, such as, oxygen, nitrogen, sulfur, silicon,phosphorus, boron and the like either may or may not be present ineither the aryl or the alkyl portion of the alkylaryl group) having fromabout 5 carbon atoms to about 100 carbon atoms, from about 5 carbonatoms to about 60 carbon atoms, from about 6 carbon atoms to about 30carbon atoms, such as tolyl or the like,

wherein the substituents on the substituted alkyl, arylalkyl andalkylaryl groups may be halogen atoms, ether groups, aldehyde groups,ketone groups, ester groups, amide groups, carbonyl groups, thiocarbonylgroups, sulfide groups, phosphine groups, phosphonium groups, phosphategroups, nitrile groups, mercapto groups, nitro groups, nitroso groups,acyl groups, acid anhydride groups, azide groups, azo groups, cyanatogroups, isocyanato groups, thiocyanato groups, isothiocyanato groups,carboxylate groups, carboxylic acid groups, urethane groups, ureagroups, mixtures thereof and the like, and wherein two or moresubstituents may be joined together to form a ring; and

X and X′ each, independently of the other, is an oxygen atom or a groupof the formula —NR₄—, wherein R₄ is:

(i) a hydrogen atom;

(ii) an alkyl group, including linear and branched, saturated andunsaturated, cyclic and acyclic, and substituted and unsubstituted alkylgroups, and wherein heteroatoms either may or may not be present in thealkyl group, having from about 5 carbon atoms to about 100 carbon atoms,from about 5 carbon atoms to about 60 carbon atoms, from about 6 carbonatoms to about 30 carbon atoms,

(iii) an aryl group, including substituted and unsubstituted arylgroups, and wherein heteroatoms either may or may not be present in thearyl group, having from about 5 carbon atoms to about 100 carbon atoms,from about 5 carbon atoms to about 60 carbon atoms, from about 6 carbonatoms to about 30 carbon atoms,

(iv) an arylalkyl group, including substituted and unsubstitutedarylalkyl groups, wherein the alkyl portion of the arylalkyl group maybe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms either may or may not be present in either thearyl or the alkyl portion of the arylalkyl group, having from about 5carbon atoms to about 100 carbon atoms, from about 5 carbon atoms toabout 60 carbon atoms, from about 6 carbon atoms to about 30 carbonatoms, or

(v) an alkylaryl group, including substituted and unsubstitutedalkylaryl groups, wherein the alkyl portion of the alkylaryl group canbe linear or branched, saturated or unsaturated, and cyclic or acyclic,and wherein heteroatoms either may or may not be present in either thearyl or the alkyl portion of the alkylaryl group, having from about 5carbon atoms to about 100 carbon atoms, from about 5 carbon atoms toabout 60 carbon atoms, from about 6 carbon atoms to about 30 carbonatoms,

wherein the substituents on the substituted alkyl, aryl, arylalkyl andalkylaryl groups may be halogen atoms, ether groups, aldehyde groups,ketone groups, ester groups, amide groups, carbonyl groups, thiocarbonylgroups, sulfate groups, sulfonate groups, sulfonic acid groups, sulfidegroups, sulfoxide groups, phosphine groups, phosphonium groups,phosphate groups, nitrile groups, mercapto groups, nitro groups, nitrosogroups, sulfone groups, acyl groups, acid anhydride groups, azidegroups, azo groups, cyanato groups, isocyanato groups, thiocyanatogroups, isothiocyanato groups, carboxylate groups, carboxylic acidgroups, urethane groups, urea groups, mixtures thereof and the like, andwherein two or more substituents may be joined together to form a ring.

In embodiments, the gellant may comprise a mixture comprising:

wherein —C₃₄H_(56+a)— represents a branched alkylene group which mayinclude unsaturations and cyclic groups, wherein the variable “a” is aninteger from 0-12.

In embodiments, the gelling agents of the ink may be compounds, asdescribed in U.S. Pat. No. 8,084,637, which is hereby incorporated byreference. For example, compounds which can be used can be of thefollowing general structures:

When present, the gelling agent or gellant can be present in amount offrom about 1 percent to about 50 percent by weight of the ink, fromabout 2 percent to about 40 percent by weight of the ink, from about 5percent to about 20 percent by weight of the total ink composition,although the amounts can be outside of those ranges.

Curable Waxes

The ink composition may optionally include at least one curable wax.Curable waxes may be made by methods as described in U.S. Publ. No.20110247521, herein incorporated by reference in entirety.

The wax may be a solid at room temperature (25° C.). Inclusion of thewax may promote an increase in viscosity of the ink composition as thecomposition cools from the application temperature. Thus, the wax mayalso assist the gellant in avoiding bleeding of the composition throughthe substrate.

The curable wax may be any wax component that is miscible with the othercomponents and will polymerize with the curable monomer to form apolymer. The term, “wax,” includes, for example, any of the variousnatural, modified natural, and synthetic materials commonly referred toas waxes.

Suitable examples of curable waxes include waxes that include or arefunctionalized with curable groups. The curable groups may include, forexample, an acrylate, methacrylate, alkene, allylic ether, epoxide,oxetane and the like. The waxes can be synthesized by the reaction of awax, such as, a polyethylene wax equipped with a carboxylic acid orhydroxyl transformable functional group. The curable waxes describedherein may be cured with the above curable monomer(s).

Suitable examples of hydroxyl-terminated polyethylene waxes that may befunctionalized with a curable group include, but are not limited to,mixtures of carbon chains with the structure, CH₃—(CH₂)_(n)—CH₂OH, wherethere is a mixture of chain lengths, n, where the average chain lengthcan be in the range of about 16 to about 50, and linear low molecularweight polyethylene, of similar average chain length. Suitable examplesof such waxes include, but are not limited to, the UNILIN series ofmaterials such as UNILIN 350, UNILIN 425, UNILIN 550, and UNILIN 700with M_(n) approximately equal to 375, 460, 550 and 700 g/mol,respectively. All of the waxes are commercially available fromBaker-Petrolite. Guerbet alcohols, characterized as2,2-dialkyl-1-ethanols, are also suitable compounds. Exemplary Guerbetalcohols include those containing about 16 to about 36 carbons, many ofwhich are commercially available from Jarchem Industries Inc., Newark,N.J., PRIPOL 2033 from Croda, Edison, N.J. and so on. For example, C-36dimer diol mixtures may be used, including isomers of the formula:

as well as other branched isomers that may include unsaturations andcyclic groups, available from Uniqema, New Castle, Del. Furtherinformation on C₃₆ dimer diols of that type is disclosed in, forexample, “Dimer Acids,” Kirk-Othmer Encyclopedia of Chemical Technology,Vol. 8, 4^(th) Ed. (1992), pp. 223 to 237, the disclosure of which isincorporated herein by reference. The alcohols can be reacted withcarboxylic acids equipped with UV curable moieties to form reactiveesters. Examples of such acids include acrylic and methacrylic acids,available from Sigma-Aldrich Co.

Suitable examples of carboxylic acid-terminated polyethylene waxes thatmay be functionalized with a curable group include mixtures of carbonchains with the structure, CH₃—(CH₂)_(n)—COOH, where there is a mixtureof chain lengths, n, where the average chain length is about 16 to about50, and linear low molecular weight polyethylene, of similar averagechain length. Suitable examples of such waxes include, but are notlimited to, UNICID 350, UNICID 425, UNICID 550 and UNICID 700 with M_(n)equal to approximately 390, 475, 565 and 720 g/mol, respectively. Othersuitable waxes have a structure, CH₃—(CH₂)_(n)—COOH, such as,hexadecanoic or palmitic acid with n=14, heptadecanoic, margaric ordaturic acid with n=15, octadecanoic or stearic acid with n=16,eicosanoic or arachidic acid with n=18, docosanoic or behenic acid withn=20, tetracosanoic or lignoceric acid with n=22, hexacosanoic orcerotic acid with n=24, heptacosanoic or carboceric acid with n=25,octacosanoic or montanic acid with n=26, triacontanoic or melissic acidwith n=28, dotriacontanoic or lacceroic acid with n=30, tritriacontanoicor ceromelissic or psyllic acid, with n=31, tetratriacontanoic or geddicacid with n=32, or pentatriacontanoic or ceroplastic acid with n=33.Guerbet acids, characterized as 2,2-dialkyl ethanoic acids, are alsosuitable compounds. Exemplary Guerbet acids include those containing 16to 36 carbons, many of which are commercially available from JarchemIndustries Inc., Newark, N.J., PRIPOL 1009 (Croda, Edison, N.J.) and soon. For example, C-36 dimer acid mixtures may also be used, includingisomers of the formula:

as well as other branched isomers that may include unsaturations andcyclic groups, available from Uniqema, New Castle, Del. Furtherinformation on such C₃₆ dimer acids is disclosed in, for example, “DimerAcids,” Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 8, 4^(th)Ed. (1992), pp. 223 to 237. The carboxylic acids can be reacted withalcohols equipped with UV curable moieties to form reactive esters.Examples of the alcohols include, but are not limited to,2-allyloxyethanol from Sigma-Aldrich Co.;

SR495B from Sartomer Company, Inc.;

CD572 (R=H, n=10) and SR604 (R=Me, n=4) from Sartomer Company, Inc.

The curable wax can be included in the composition in an amount of from,for example, about 0.1% to about 30% by weight of the composition, fromabout 0.5% to about 20%, from about 0.5% to 15%.

Initiators

The radiation-curable gel ink may optionally include an initiator, suchas, for example, a photoinitiator. An initiator can assist in curing theink.

In embodiments, a photoinitiator that absorbs radiation, for example, UVlight radiation, to initiate curing of the curable components of the inkmay be used. Ink compositions containing acrylate groups or inkscomprised of polyamides may include photoinitiators such asbenzophenones, benzoin ethers, benzil ketals, α-hydroxyalkylphenones,α-alkoxyalkylphenones α-aminoallylphenones and acylphosphinephotoinitiators sold under the trade designations of IRGACURE andDAROCUR from Ciba. Specific examples of suitable photoinitiators include2,4,6-trimethylbenzoyldiphenylphosphine oxide (available as BASF LUCIRINTPO); 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (available asBASF LUCIRIN TPO-L); bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine oxide(available as Ciba IRGACURE 819) and other acyl phosphines;2-methyl-1-(4-methylthio)phenyl-2-(4-morpholinyl)-1-propanone (availableas Ciba IRGACURE 907) and1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methylpropan-1-one (availableas Ciba IRGACURE 2959); 2-benzyl 2-dimethylamino1-(4-morpholinophenyl)butanone-1 (available as Ciba IRGACURE 369);2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)-benzyl)-phenyl)-2-methylpropan-1-one(available as Ciba IRGACURE 127);2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-ylphenyl)-butanone(available as Ciba IRGACURE 379); titanocenes; isopropylthioxanthone;1-hydroxy-cyclohexylphenylketone; benzophenone;2,4,6-trimethylbenzophenone; 4-methylbenzophenone;diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide;2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester;oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone);2-hydroxy-2-methyl-1-phenyl-1-propanone; benzyl-dimethylketal; andmixtures thereof. Mention may also be made of amine synergists, i.e.,co-initiators that donate a hydrogen atom to a photoinitiator andthereby form a radical species that initiates polymerization (aminesynergists can also consume oxygen dissolved in the ink as oxygeninhibits free radical polymerization), for example,ethyl-4-dimethylaminobenzoate and 2-ethylhexyl-4-dimethylaminobenzoate.Any known photoinitiator that initiates free radical reaction onexposure to a desired wavelength of radiation, such as, UV light, can beused without limitation.

In embodiments, the photoinitiator may absorb radiation of about 200 toabout 420 nm to initiate cure, although use of initiators that absorb atlonger wavelengths, such as, the titanocenes that may absorb up to 560nm, may also be used without restriction.

The total amount of initiator included in the ink composition may befrom, for example, about 0.5 to about 15% by weight of the inkcomposition, from about 1 to about 10%.

Colorants

In embodiments, the green solid ink includes at least one colorant or amixture of two or more colorants. As used herein the term, “colorant,”includes pigments, dyes, mixtures of dyes, mixtures of pigments,mixtures of dyes and pigments, and the like.

In embodiments, “green,” inks may be produced that match PANTONE® Greenwhen printed on standard paper. The inks use standard pigments that arelight-fast and known to be compatible with the ink formulation.

Measurement of the color can, for example, be characterized by CIEspecifications, commonly referred to as CIE L*, a*, b*, where L*, a*,and b* are the modified opponent color coordinates, which form a 3dimensional space, with L* characterizing the lightness of a color, a*approximately characterizing the redness/greenness, and b* approximatelycharacterizing the yellowness/blueness of a color. The pigmentconcentration is chosen so that lightness (L*) corresponds with thedesired ink mass on the substrate. All of the parameters may be measuredwith any industry standard spectrophotometer including those obtained,for example, from X-Rite Corporation. Color differences may bequantified as ΔE, or the color difference between a sample color and areference color. ΔE may be calculated by any acceptable formula known inthe art, for example, by using the CIE ΔE2000 formula. The L*, a* and b*data required for determining ΔE₂₀₀₀ may be calculated, for example,under D50 illuminant and 2° observer, using Reflectance spectra whichmay be measured with a spectrophotometer, for example, a GretagMacbethSPECTROLINO® spectrophotometer.

In green solid ink compositions, the target color for the green may beselected to substantially match or substantially be the same as thecolor PANTONE® Green. Colors are, “substantially,” the same when thecolors have a ΔE₂₀₀₀ color difference of less than about 5, such as lessthan about 3, less than about 2, less than about 1. Thus, a green inkmay include, for example, inks having similar color compared to theconventional PANTONE® Green color. Thus, in embodiments, the green inksachieve the above L* values and match the color of a particular tint ofthe conventional PANTONE® Green.

In embodiments, green inks may be produced by combining a green colorantwith an optional hue-adjusting colorant and an optional shade-adjustingcolorant. Each of the green, hue-adjusting and shade-adjusting colorantsmay be a single colorant or a combination of colorants, although thegreen, hue-adjusting and shade-adjusting colorants may differ from eachother.

In embodiments, the green inks disclosed herein may contain any suitablegreen colorant. Green colorants include a colorant or combination ofcolorants that show spectral reflectance wavelengths of light from about480 nm to about 530 nm Green colorants may include colorants, such as,Hostaperm Green, Phthalo Green 5319P, Phthalo Green 5319D, Phthalo Green5319S, Winsor Green, Phthalocyanine Green G, Copper PhthalocyanineGreen, C.I. Pigment Green 42, Non-flocculating Green G, Polychlorocopper phthalocyanine, C.I. 74260 and combinations thereof.

Hue-adjusting colorants for a green ink may include a colorant orcombination of colorants composed of at least green pigment. Thehue-adjusting colorant may be present in an amount of from about 0.001%to about 1% by weight of the ink, from about 0.04% to about 0.2% byweight of the ink.

In embodiments, shade-adjusting colorants for a green ink may include acolorant or combination of colorants that absorb wavelengths of lightfrom about 400 to about 500 nm. More specifically, shade-adjustingcolorants with a spectral reflectance of light in the wavelength rangefrom about 450 to about 560 nm may be used.

The total colorant may comprise from about 0.1% to about 10% by weightof the ink, from about 0.2% to about 5% by weight of the ink.

Colorants suitable for use herein include pigment particles having anaverage particle size of from about 15 nm to about 500 nm, from about 50nm to about 200 nm in volume average diameter.

Additional Additives

The ink vehicles of embodiments may be mixtures of curable componentsand, optionally, additional materials including curable solids,antioxidants, non-photoinitiated activators (e.g., MARK® K 102, MARK® K104 and ACTAFOAM® R-3, all commercially available from Compton Corp.),as well as any conventional optional additives. Such conventionaladditives may include, for example, defoamers, slip and leveling agents,pigment dispersants, surfactants, optical brighteners, thixotropicagents, dewetting agents, slip agents, foaming agents, antifoamingagents, flow agents, waxes, oils, plasticizers, binders, electricalconductive agents, fungicides, bactericides, organic and/or inorganicfiller particles, UV absorbers, leveling agents, opacifiers, antistaticagents, and the like. The inks may also include additional monomeric,oligomeric, or polymeric materials as desired.

Curable Solids

Curable solids include radiation-curable materials that are solids atroom temperature and have one or more unsaturated functional groupstherein, such as, one or more alkene, alkyne, acrylate or methacrylatereactive groups. In embodiments, the curable solids are low molecularweight curable solids. As used herein, the term, “low molecular weight,”refers to compounds having a weight average molecular weight of about500 daltons or less, about 150 to about 450 daltons, from about 200 toabout 400 daltons.

In embodiments, the curable solid is an alkyl acrylate, aryl acrylate,alkylaryl acrylate, aryl alkyl acrylate, alkyl methacrylate, arylmethacrylate, alkylaryl methacrylate or aryl alkyl methacrylate.

The curable solid may be present in any effective amount of the curableinkjet ink compositions, such as, for example, from about 25 wt % toabout 75 wt %, from about 30 wt % to about 70 wt %, from about 40 wt %to about 70 wt % of the overall weight of the ink.

Antioxidants

The radiation-curable gel ink compositions can also optionally containan antioxidant. The optional antioxidants of the ink compositionsprotect the images from oxidation and also protect the ink componentsfrom oxidation during the heating portion of the ink preparationprocess. Specific examples of suitable antioxidant stabilizers includeNAUGARD 524, NAUGARD 635, NAUGARD A, NAUGARD 1-403, and NAUGARD 959,commercially available from Crompton Corporation, Middlebury, Conn.;IRGANOX 1010, and IRGASTAB UV 10, commercially available from CibaSpecialty Chemicals; GENORAD 16 and GENORAD 40 commercially availablefrom Rahn AG, Zurich, CH and the like.

When present, the optional antioxidant is present in the inkcompositions of embodiments in any desired or effective amount, such as,at least about 0.01% by weight of the ink composition, at least about0.1% by weight of the ink composition, at least about 1% by weight ofthe ink composition.

Ink Preparation

In embodiments, the radiation-curable gel inks may be prepared by anysuitable technique. For example, the inks may be prepared by mixing theinitiator, monomer, optional gellant and the curable wax; and heatingthe mixture to obtain a single phase with low viscosity. Thereafter, thehot mixture is slowly added to a heated colorant (i.e. pigment)dispersion (which may be a concentrate) while agitating the mixture. Theink composition may then be, optionally at an elevated temperature,passed through a filter to remove extraneous particles.

The method of preparation for the ink compositions may be modified so asto accommodate the type of reactive gelling agents used for thepreparation of the ink compositions. For example, a concentrate of thegelling agent may be prepared in one of the components of the inkcomposition prior to the addition of the other components. Solutionscontaining co-gelling agents can also be prepared by a method similar tothe one described above. Further examples of ink preparation methods areset forth in the Examples below.

In embodiments, the ink compositions may have gelling temperatures offrom about 30° C. to about 75° C., from about 30° C. to about 70° C.,from about 35° C. to about 70° C. Generally, the ink composition is agel at room temperature.

In embodiments, when the ink composition is in the gel state, theviscosity of the ink composition is at least about 1,000 mPas, at leastabout 10,000 mPas, at least about 100,000 mPas. The viscosity values inthe gel state of exemplary ink compositions may be in the range of fromabout 10³ to about 10⁹ mPas, from about 10^(4.5) to about 10^(6.5) mPas.Gel phase viscosity of embodiments can vary with the print process. Forexample, the highest viscosities may be suitable for use in embodimentsthat employ intermediate transfer or when jetting directly to porouspaper to minimize the effects of ink bleed and feathering. On the otherhand, less porous substrates, such as plastic, may require lowerviscosities that control dot gain and agglomeration of individual inkpixels. The gel viscosity can be controlled by ink composition andsubstrate temperature. An additional benefit of the gel state forradiation-curable gellant-containing ink compositions is that higherviscosities of about 10³-10⁴ mPas can reduce oxygen diffusion, which, inturn leads to a faster rate of cure in free radical initiation.

When the ink composition is at jetting temperature, the ink compositionhas a viscosity of less than about 15 mPas, less than about 12 mPas,from about 3 to about 12 mPas, from about 5 to about 10 mPas. Inembodiments, the ink compositions are jetted at temperatures of lessthan about 100° C., from about 40° C. to about 100° C., from about 55°C. to about 90° C.

In embodiments, the green gel ink when printed on paper has a mass offrom about 0.1 to about 1.5 mg/cm², from about 0.4 to about 0.7 mg/cm².

Image Forming and Inkjet Devices

Gel ink jet printing process and apparatuses are well known in the artand may include either direct or indirect image formation.

Printed images may be generated with the ink described herein byincorporating the ink into an inkjet device, such as, a thermal inkjetdevice, an acoustic inkjet device or a piezoelectric inkjet device, andconcurrently causing droplets of molten ink to be ejected in animagewise manner onto a substrate. In embodiments, the ink may be heatedto a jetting temperature, for instance, above the gel-transitiontemperature of the ink composition.

In embodiments, the substrate may be at any suitable temperature duringrecording. The recording substrate may be at room temperature. However,in some embodiments, the substrate may be heated or cooled to have asurface temperature that is, for example, within the range of gel phasetransition temperatures for the ink composition. For example, thesubstrate may be maintained at a temperature of from about 5° C. toabout 160° C., from about 15° C. to about 50° C., from about 20° C. toabout 40° C.

The ink is typically included in at least one reservoir connected by anysuitable feeding device to the ejecting channels and orifices of aninkjet head. In the jetting procedure, the inkjet head may be heated, byany suitable method, to the jetting temperature of the inks. The inkreservoir(s) may also include heating elements to heat the ink. The UVinks are thus transformed from the gel state to a molten state forjetting. “At least one,” or, “one or more,” as used to describecomponents of the inkjet device, such as the ejecting channels,orifices, etc., refers to from 1 to about 2 million, from about 1000 toabout 1.5 million, from about 10,000 to about 1 million of any suchcomponent found in an inkjet device. “At least one,” or, “one or more,”as used to describe other components of the inkjet device such as theinkjet head, reservoir, feeder etc., and refers to from 1 to about 15,from 1 to about 8, from 1 to about 4 of any such component found in theinkjet device.

The inks may also be employed in indirect (offset) printing ink jetapplications, where droplets of the melted ink are ejected in animagewise manner onto an intermediate transfer member and the ink in theimagewise pattern is subsequently transferred from the intermediatetransfer member to a final recording substrate. An exemplary offset orindirect printing process is disclosed in U.S. Pat. No. 5,389,958, thedisclosure of which is incorporated herein by reference.

The intermediate transfer member may take any suitable form, such as, adrum or a belt. The member surface may be at room temperature or may beheated to have a surface temperature, for example, within the gel statetemperature range for the ink composition. For example, the surface maybe maintained at a temperature of about 25° C. to about 100° C., fromabout 30° C. to about 70° C., from about 30° C. to about 50° C. Hence,the jetted ink may be made to rapidly form a gel, which gel ismaintained on the surface of the transfer member until transfer to theimage-receiving substrate. Thus, the ink may be heated to a jettingtemperature, for instance, above the gel transition temperature of theink composition and then heated to a second temperature at which the gelforms that is less than the first temperature.

Once on the intermediate transfer member surface, the jetted ink may beexposed to a limited extent of radiation so as to effect a limitedcuring of the ink on the intermediate transfer member surface. Theintermediate curing does not fully cure the ink, but merely assists insetting the jetted ink so that the ink may be transferred to the imagereceiving substrate with the appropriate amount of penetration, whichrequires the ink droplets to have a certain rheology before transfer.For controlling the extent of the curing if an intermediate cure ispracticed, reference is made to US Publ. Nos. 2006/0158496 and2006/0119686, each incorporated herein by reference. The intermediatecuring step is not necessary, such as, when the gel state is sufficientto impart the desired rheology to the ink droplets.

Following jetting to the intermediate transfer member and optionalintermediate curing thereon, the ink composition is then transferred toa suitable substrate.

The ink can be jetted or transferred onto any suitable substrate orrecording sheet to form an image including plain papers, such as, XEROX4200 papers, XEROX Image Series papers, Courtland 4024 DP paper, rulednotebook paper, bond paper and the like; silica-coated papers, such as,Sharp Company silica-coated paper, JuJo paper, HAMMERMILL LASERPRINTpaper and the like; glossy papers, such as, XEROX Digital Color Gloss,Sappi Warren Papers LUSTROGLOSS and the like; transparency materials;fabrics; textile products; plastics; polymeric films; inorganicsubstrates such as metals, ceramics, wood; and the like.

Following transfer to the substrate or jetting to the substrate ifdirect printing is employed, the ink is cured by exposing the image onthe substrate to radiation. For example, radiation having an appropriatewavelength, mainly the wavelength at which the ink initiator absorbsradiation, may be used. That initiates the curing reaction of the inkcomposition. The radiation exposure need not be long and may occur fromabout 0.05 to about 10 seconds, from about 0.2 to about 2 seconds. Theexposure times are more often expressed as substrate speeds of the inkcomposition passing under a UV lamp. For example, the microwaveenergized, doped mercury bulbs available from UV Fusion are placed in anelliptical mirror assembly that is 10 cm wide; multiple units may beplaced in series. Thus, a belt speed of 0.1 ms⁻¹ would require 1 secondfor a point on an image to pass under a single unit, while a belt speed4.0 ms⁻¹ would require 0.2 seconds to pass under four bulb assemblies.

In embodiments, the energy source used to initiate crosslinking of theradiation-curable components of the composition may be actinic, such as,radiation having a wavelength in the ultraviolet or visible region ofthe spectrum; accelerated particles, such as, electron beam radiation;thermal, such as, heat or infrared radiation; or the like. Actinicradiation provides excellent control over the initiation and rate ofcrosslinking. Suitable sources of actinic radiation include mercurylamps, xenon lamps, carbon arc lamps, tungsten filament lamps, lasers,light emitting diodes, sunlight, electron beam emitters and the like.The curing light may be filtered or focused, if desired or necessary.

The curable components of the ink composition react to form a cured orcross-linked network of appropriate hardness and robustness. Inembodiments, the curing is substantially complete to complete, i.e., atleast 75% of the curable components are cured (reacted and/orcross-linked). That allows the ink composition to be substantiallyhardened and much more scratch resistant, and also adequately controlsthe amount of show-through on the substrate.

The following examples of radiation-curable gel ink compositions furtherillustrate the foregoing embodiments. The Examples are illustrative ofdifferent compositions and conditions that can be utilized in practicingthe disclosure. It will be apparent, however, that the disclosure can bepracticed with many types of compositions and can have many differentuses in accordance with the disclosure above.

EXAMPLES Example 1 Preparation of Ink Base

The inks were prepared with an amide gellant. UNILIN 350 acrylate wax(optionally prefiltered to 2 μm) was the curable wax. The ink carriercomprised SR833S (Sartomer). The initiators were selected from Irgacure379, Esacure KIP 150 (Lamberti) and Irgacure 819, Ciba. The stabilizerwas Irgastab UV10 (Ciba).

Synthesis of Amide Gellant Precursor

The synthesis of the amide gellant precursor (organoamide) is aspracticed in U.S. Pat. No. 8,084,637, for example, reacting a dimerdiacid, such as, Pripol 1009 (Cognis Corp.) with ethylenediamine (EDA)at a temperature of between about 90° C. to about 155° C., optionally inthe presence of an antioxidant/stabilizer, such as, Irgafos 168 (Ciba)in an amount of about 0.2%. Oligomers are created during preparation ofthe organoamide (end-capping to make the esters in the final gellantdoes not change the oligomer distribution).

By controlling the amount of EDA, the distribution can be shifted tocreate larger proportions of higher order oligomers. Generally, withhigher EDA:amide ratios, a higher gel point and room temperatureviscosity is observe

An amide gellant precursor using an EDA:Pripol 1009 ratio of 1.125:2 wasprepared by adding to a 2L stainless steel reactor equipped with bafflesand 4-blade impeller, Pripol 1009 dimer diacid (703.1 g, acid number=194mg/g, 1215 mmol). The reactor was purged with argon, heated to 90° C.and the impeller was set to 400 RPM. Next, EDA (Huntsman ChemicalCorporation, 21.9 g, 364 mmol) was added slowly through a feed linedirectly into the reactor over 15 minutes. The reactor temperature wasset at 95° C. Next, the reactor temperature was ramped up to 165° C.over 280 minutes and held at 165° C. for 1 hour. Finally, the moltenorganoamide product was discharged into a foil pan and allowed to coolto room temperature. The product was an amber-coloured solid resin withan acid number of 133.7 mg/g.

The acid termini of the precursor was end-capped with phenyl glycolfollowing the materials and methods provided in U.S. Pat. No. 8,084,637.The oligomeric distributions for the amide gallant is summarized inTable 1.

A baseline amide gellant precursor using an EDA:Pripol 1109 ratio of1.125:2 was prepared as follows. To a 2L stainless steel Buchi reactorequipped with 4-blade steel impeller, baffle, and condenser was addedthe organoamide prepared above (711.8 g, acid number of 133.7, 614.65mmol) via the addition port and using a heat gun to melt the materials.Next, the reactor was purged with N₂ at 3 SCFH (standard cubic feet perhour) flow rate, heated to 210° C. and mixing at 450 RPM. Next,2-phenoxyethanol (281.2 g, 2035.4 mmol, Aldrich Chemicals) and Fascat4100 (0.70 g, 2.05 mmol, Arkema Inc.) were premixed in a beaker, andadded to the reaction. The reaction port was closed and the reaction washeld at 210° C. for 2.5 hours. The reactor port was opened and anadditional 27.5 g of phenoxyethanol were added and the reaction wasallowed to run for 4 hours. After the reaction was completed, the moltengellant product was discharged into a foil pan and allowed to cool toroom temperature. The product was an amber-colored firm gel with an acidnumber of 3.9 mg/g.

TABLE 1 Mw Distributions by MALDI-TOF of Amide Gellant n Name AmideGellant 0 Unimer 26.7 1 Dimer 57.6 2 Trimer 14.7 3 Tetramer 0.9Synthesis of UNILIN® 350 Acrylate at 5 gal Scale

About 5.4 kg of UNILIN® 350, 6.8 g of hydroquinone, 53.5 g of p-toluenesulfonic acid and 1.1 kg of toluene were charged through the charge portinto a reactor. The charge port was closed and the reactor was heated toa jacket temperature of 120° C. Agitation was begun at minimum once thereactor contents reached a temperature of approximately 65° C. Once theinternal reactor temperature reached 85° C., signaling that the solidshave melted, agitation was increased to 150 rpm. The final two reagentswere added via a Pope tank. First, 1.32 kg of acrylic acid were addedand then the Pope tank and lines were rinsed through the reactor with1.1 kg of toluene. The time of acrylic acid addition was marked as timezero. The jacket temperature was then ramped from 120° C. to 145° C.over 120 minutes. That was done manually with an increase of 2° C. every10 minutes. During that time, reaction condensate (water) was cooled andcollected by a condenser. Approximately 200 g of water were collected.Also, approximately 1.1 kg of toluene (50% of the charge) were removedby distillation along with the reaction condensate.

Once the reactor jacket reached the maximum temperature of 145° C.,cooling was begun to bring the reactor to a batch temperature of 95° C.Agitation was reduced to 115 rpm. About 23 kg of deionized water (“DIW”)were brought to boil and then charged to the reactor via the Pope tank(temperature of water by the time of transfer was greater than 90° C.).Mixing continued for 30 seconds and, after mixing was stopped, the waterand waxy acrylate phases were allowed to separate. The bottom (water)phase was discharged to a steel pail from the bottom valve using thesight glass to monitor the interface. The extraction procedure wasrepeated with another 2.7 kg of hot DIW and the water discharged to apail. A third and final extraction was conducted with 10 kg of hot DIW,separated but not discharged to a pail. Instead, the hot water layer wasused to preheat the discharge line to a vacuum filter.

At the start of the experiment day, preparations were made to a vacuumfilter for the discharge and precipitation steps. The filter was chargedwith 100 kg of DIW. Deionized cold water cooling and agitation atminimum were begun to the jacket of the filter to facilitate cooling theDIW to less than 10° C. for product solidification.

Following the third extraction, maximum agitation was begun to thefilter. The reactor, the filter and the discharge lines were all checkedfor proper bonding and grounding, and both vessels were purged withnitrogen to ensure an inert atmosphere. The reactor was isolated and amoderate (10 SCFH) nitrogen blanket on the filter was begun, and wasmaintained throughout the discharge procedure.

After the final 10 minutes of separation time and once Tr=95° C., 5 kPaof nitrogen pressure were applied to the reactor. That ensured an inertatmosphere throughout the discharge procedure. The bottom valve wasopened slightly and the hot reactor contents were slowly poured into thefilter. The first layer was water and the next layer, the desired UNILIN350 acrylate, which solidified into yellowish white particles. Once thedischarge was complete, all nitrogen purges was stopped and both vesselsvented to the atmosphere. Agitation continued on the filter forapproximately 10 minutes. A flexible transfer line was connected fromthe central vacuum system to a waste receiver. Full vacuum was appliedto the waste receiver, then the bottom valve of the filter was opened tovacuum transfer the water filtrate.

Once a dried sample of the material had an acid number of <1.5, thebatch was discharged by hand into foil-lined trays, and dried in avacuum oven at 55° C. with full vacuum overnight. The next day, the drymaterial was discharged and stored in 5 gallon pails. The yield from thebatch was approximately 5.2 kg.

Inks were each prepared on a 20 gram scale by combining all components,except the pigment dispersion, and mixing the components at 90° C. and200 rpm for approximately 1 hour. After 1 hour, the pigment dispersionwas added to each ink and the combined ink composition was stirred at90° C. for an additional hour. The inks were fully miscible, givingsolutions with a pourable viscosity at elevated temperatures and formingstiff gels when cooled to room temperature.

Green Pigment Dispersion Preparation

Into a 1 liter Attritor (Union Process) were added 1200 grams stainlesssteel shots (⅛ inch diameter), 30 grams Hostaperm Green GNX pigment(Pigment Green 7, Clariant), 18 grams EFKA 4340 dispersant, neat (BASF)and 152 grams SR9003 monomer (Sartomer). The mixture was stirred for 18hours at 400 RPM, and then discharged into a 200 mL container. Theresulting pigment dispersion has a pigment concentration of 15 weightpercent.

Ink Preparation

Various UV curable phase change ink compositions were prepared asfollows: to a 250 mL amber glass bottle heated to 90° C. were addedamide gellant, acrylated Unilin 350 wax, SR833S monomer (tricyclodecanedimethanol diacrylate, Sartomer, Exeter, Pa.), SR399LV (pentafunctionalacrylate ester, Sartomer), Irgaure 379 and 819 (photoinitiators, CIBA),Esacure KIP 150 (photoinitiator, Lamberti) and Irgastab UV10(stabilizer, CIBA). The mixture was heated with stirring until the solidcomponents were dissolved. The mixture was heated with stirring for 1hour to complete the ink base preparation. Finally, a green pigmentdispersion concentrate in SR9003 (propyxlated neopentyl glycoldiacrylate, Sartomer) was added and the mixture was homogenized at10,000 RPM for an additional 0.5 hours. About 7.5 g of amide gellant, 5g of UNILIN 350 acrylate, 3 g of IRGACURE® 379 (Ciba), 0.5 g ofIRGACURE® 819, 4 g Esacure KIP 150 (Lamberti), 0.2 g of IRGASTAB® UV10,5 g of SR399LV (Sartomer Company, Inc.), 48.1 g of SR833S (SartomerCompany, Inc.) were mixed at 90° C. for 1 h. The ink base was filteredthrough a 1 μm stacked filter. The filtered ink base was added to acolorant mixture as shown in Table 1 and additional SR833S as requiredto make-up the mass balance, while stirring at 90° C. The resulting inkis stirred at 90° C. for 2 h, before filtration through a 1 μm filter.

TABLE 2 Green UV Gel Ink, 4 weight % Pigment Green 7 Green UV Gel InkComponent wt % m/g Amide Gellant  7.50% 7.5 Unilin 350 Acrylate  5.00%5.0 SR833S 48.13% 48.1 SR399LV  5.00% 5.0 Irgacure 379  3.00% 3.0Irgacure 819  0.50% 0.5 Esacure KIP 150  4.00% 4.0 Irgastab UV10  0.20%0.20 Green pigment dispersion 26.67% 26.7 TOTAL  74.8% 100.0

Inks were printed on uncoated Mylar sheets using a Typhoon print headand cured with a 600 W Fusions UV Lighthammer UV curing lamp fitted witha mercury D bulb under a moving conveyor belt moving at various speeds(feet per minute—fpm). The cured films were subjected to double MEK rubswith a cotton swab to evaluate cure. The table below summarizes the filmMEK rub resistance properties. A good curing ink is considered one inwhich the double MEK rubs exceed 150 at all speeds. The green UV gelinks have superior cure properties.

TABLE 3 Double rub results at various cure speeds Sample 32 fpm 90 fpm150 fpm 240 fpm Green UV Gel Ink 200 200 200 200

Color was measured preparing solid patch prints on DCEG paper. Dropmass, pigment concentration and resolution are provided in Table 4.

TABLE 4 Color for Green UV Gel Ink Drop Ink Pigment ΔE₂₀₀₀ Pigment MassConcentration Concentration relative to wt % Resolution (ng) (mg/inch²)(mg/inch²) L* a* b* PANTONE ® Green 4 600 × 500 16.5 5.94 0.238 58.84−73.8 4.1 2.76 UV Gel Ink

Prints were measured using a Spectrolino spectrophotometer, D50 lightsource, 2°. Table 3 above shows the pigment concentration on the solidfill image, as well as L*, a* and b* values, and ΔE₂₀₀₀ relative toPANTONE® Green. The UV ink was jetted successfully and solid patcheswere measured to be all below ΔE₂₀₀₀ of 4 which is desired. Reflectancecurves for the UV ink printed as a solid patch and PANTONE® Green weresubstantially identical. Table 4 shows the reflectance % at keywavelengths of light for the green color.

TABLE 5 Spectral Reflectance for Green UV Ink. Spectral Reflectance %Wavelength 500 600 Green UV Ink 54.3% 3.1%

The reflectance percents at the listed wavelengths are critical toachieve the proper color for green. Graphtol pigments from Clariant arecompared and the test for lightfastness was determined on artificiallight in accordance with DIN ISO 12 040 (XENONTEST 1200 W, nonturning-mode).

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

We claim:
 1. A green radiation-curable lightfast gel ink, comprising: atleast one curable monomer, at least one organic gellant, at least onephotoinitiator and a green colorant selected from the group consistingof Hostaperm green, Phthalo Green 5319P, Phthalo Green 5319D, PhthaloGreen 5319S, Winsor Green, Phthalocyanine Green G, Copper PhthalocyanineGreen, C.I. Pigment Green 42, Non-flocculating Green G, Polychlorocopper phthalocyanine, C.I. 74260 and combinations thereof, wherein theink exhibits a reflectance on a substrate at a loading of from about 2mg/inch² to about 7 mg/inch² that ranges from 50% to about 60% at awavelength of 500 nm and that ranges from 0% to about 10% at awavelength of about 600 nm, and wherein the radiation curable inkmatches PANTONE® green in color within a ΔE₂₀₀₀ of about 4 or less. 2.The radiation curable ink of claim 1, wherein the radiation isultraviolet (UV) having a wavelength of about 200 to about 400 nm. 3.The radiation curable ink of claim 1, wherein said ink on said substrateexhibits an L* from about 55 to about
 65. 4. The radiation curable inkof claim 1, wherein said ink on said substrate exhibits an a* less thanabout −70.
 5. The radiation curable ink of claim 1, wherein the gellantis an amide gellant.
 6. The radiation curable ink of claim 1, whereinthe colorant is Hostaperm green GNX.
 7. The radiation curable ink ofclaim 1, wherein the substrate is selected from the group consisting ofpaper, metal, plastic, membrane and combinations thereof.
 8. Theradiation curable ink of claim 1, wherein the colorant is present in anamount of from about 0.05% to about 6% by weight of the ink.
 9. Theradiation curable ink of claim 1, wherein the at least one curablemonomer is selected from the group consisting of propoxylated neopentylglycol diacrylate, diethylene glycol diacrylate, triethylene glycoldiacrylate, hexanediol diacrylate, dipropyleneglycol diacrylate,tripropylene glycol diacrylate, epoxylated neopentyl glycol diacrylate,isodecyl acrylate, tridecyl acrylate, isobornyl acrylate,isobornyl(meth)acrylate, propoxylated trimethylolpropane triacrylate,ethoxylated trimethylolpropane triacrylate, di-trimethylolpropanetetraacrylate, dipentaerythritol, pentaacrylate, ethoxylatedpentaerythritol tetraacrylate, propoxylated glycerol triacrylate,isobornyl methacrylate, lauryl acrylate, lauryl methacrylate, neopentylglycol propoxylate methylether monoacrylate, isodecylmethacrylate,caprolactone acrylate, 2-phenoxyethyl acrylate, isooctylacrylate,isooctylmethacrylate and combinations thereof.
 10. The radiation curableink of claim 1, further comprising a wax.
 11. The radiation curable inkof claim 1, further comprising a non-photoinitiated activator.
 12. Theradiation curable ink of claim 1, wherein the radiation curable inkexhibits lightfastness of 6 or greater on the Blue Wool Scale.
 13. Theradiation curable ink of claim 1, wherein the radiation curable inkexhibits a double MEK rub of about 200 at 32 feet per minute (fpm), 90fpm, 150 fpm, or 240 fpm.
 14. A method of making a greenradiation-curable ink comprising: mixing at least one curable monomer,at least one organic gellant, at least one photoinitiator, and at leastone green colorant selected from the group consisting of Hostapermgreen, Phthalo Green 5319P, Phthalo Green 5319D, Phthalo Green 5319S,Winsor Green, Phthalocyanine Green G, Copper Phthalocyanine Green, C.I.Pigment Green 42, Non-flocculating Green G, Polychloro copperphthalocyanine, C.I. 74260 and combinations thereof, wherein the inkexhibits a reflectance on a substrate at a loading of from about 2mg/inch² to about 7 mg/inch² that ranges from 50% to about 60% at awavelength of 500 nm and that ranges from 0% to about 10% at awavelength of about 600 nm; heating the mixture; and cooling the heatedmixture to form a gel ink, wherein the resulting ink matches PantoneGreen in color within a ΔE₂₀₀₀ of about 3 or less.
 15. The method ofclaim 14, further comprising filtering the resulting ink.
 16. The methodof claim 14, wherein the at least one curable monomer is selected fromthe group consisting of propoxylated neopentyl glycol diacrylate,diethylene glycol diacrylate, triethylene glycol diacrylate, hexanedioldiacrylate, dipropyleneglycol diacrylate, tripropylene glycoldiacrylate, epoxylated neopentyl glycol diacrylate, isodecyl acrylate,tridecyl acrylate, isobornyl acrylate, isobornyl(meth)acrylate,propoxylated trimethylolpropane triacrylate, ethoxylatedtrimethylolpropane triacrylate, di-trimethylolpropane tetraacrylate,dipentaerythritol pentaacrylate, ethoxylated pentaerythritoltetraacrylate, propoxylated glycerol triacrylate, isobornylmethacrylate, lauryl acrylate, lauryl methacrylate, neopentyl glycolpropoxylate methylether monoacrylate, isodecylmethacrylate, caprolactoneacrylate, 2-phenoxyethyl acrylate, isooctylacrylate,isooctylmethacrylate, and combinations thereof.
 17. The method of claim14, wherein the colorant is Hostaperm green GNX, and wherein thecolorant concentration on the substrate by weight is about 0.2 mg/inch²or greater.
 18. The method of claim 14, wherein said ink on saidsubstrate exhibits an L* satisfying the relationship:55<L*<65; and exhibits an a* satisfying the relationship:a*<−68.
 19. The method of claim 14, wherein the radiation curable inkexhibits a double MEK rub of about 200 at 32 feet per minute (fpm), 90fpm, 150 fpm, or 240 fpm.